Di-tert-butyl dicarbonate (Boc2O, 25.73 g, 117.88 mmol) was added slowly and dropwise at 0 °C to dichloromethane (DCM, containing 8-bromo-1,2,3,4-tetrahydroisoquinoline (Intermediate 21, 25.00 g, 117.88 mmol) and triethylamine (TEA, 32.83 mL, 236.00 mmol) in a 300 mL) solution. The reaction mixture was stirred continuously for 30 minutes at room temperature. Upon completion of the reaction, citric acid solution was added to quench the reaction, followed by a layering operation. The organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate, 3/1, v/v) to afford N-boc-8-bromo-1,2,3,4-tetrahydroisoquinoline (Intermediate 22, 35 g, 95% yield).
